BLOODVESSELS OF THE KIDNEY. 103 



thus reaches the fasciculus of tubules, so do they successively 

 break up into capillaries. The number of the arteriolse conse- 

 quently diminishes towards the papillae, until in the latter only 

 one or two remain, which break up into capillaries, and are 

 distributed over the papillae themselves. 



The capillary plexus investing the urinary tubules of the 

 medulla is wide-meshed, and, as has been already mentioned, 

 when it is in immediate contact with the cortex, is uninter- 

 ruptedly continuous with the capillaries of this region of the 

 cortex. 



In consequence of this arrangement the supply of blood to 

 the medullary portion is partially independent of that of the 

 cortex, and the former would still continue to obtain its supply 

 even if all the cortical vessels were obliterated; on the other 

 hand, the medullary portion is to some extent dependent on 

 the vascular supply of the cortex, since it receives at least 

 a portion of the blood circulating through the vasa efferentia 

 of those glomeruli from which the arteriolas rectse proceed. 

 The blood issuing from the glomeruli does not, however, always 

 pass through the medullary portion, since it not unfrequently 

 happens that a vas efferens, before it gives off arteriolse rectae, 

 supplies branches to the tortuous portions of the tubules that 

 break up into capillaries in the same manner as in other parts 

 of the cortex. 



The veins of the medullary portion run in the same fissures 

 as the arteries. The structure of their walls differs from that 

 of other veins of the same size, in the circumstance that the 

 cells of their endothelial lining are extraordinarily elongated 

 in the direction of the axis of the vessel. To so great an 

 extent does this take place in some instances, that the wall of 

 the vessel presents the appearance of being composed of fibres. 

 The venulye rectse so far pursue the same course as the arteries 

 of the same name, that the several trunklets originating in the 

 coalescence of a capillary circle do not immediately unite to 

 larger trunks, but remain separate as far as to the cortical 

 surface of the intermediate layer. But inasmuch as a small 

 venous plexus is already present upon the papilla around the 

 openings of the ductus papillares, that principally discharges 

 its contents through the medulla, a few small venous trunks 



